New enzymes for cheaper biofuel production engineered

March 24th, 2009 - 5:02 pm ICT by ANI  

Washington, Mar 24 (ANI): Researchers at the California Institute of Technology (Caltech) and world-leading gene-synthesis company DNA2.0 have created new enzymes for cheaper biofuel production.
Biofuels are made by converting renewable materials–for example, corn kernels, wood chips left over from pulp and paper production, prairie grasses, and even garbage–into fuels and chemicals.
Frances H. Arnold, the Dick and Barbara Dickinson Professor of Chemical Engineering and Biochemistry at Caltech, and her colleagues have constructed 15 new highly stable fungal enzyme catalysts that efficiently break down cellulose into sugars at high temperatures.
Cellulose is the world’’s most abundant organic material and cheapest form of solar-energy storage.
Plant sugars are easily converted into a variety of renewable fuels such as ethanol or butanol.
Earlier, less than 10 such fungal cellobiohydrolase II enzymes were known.
But the new enzymes, not only boast remarkable stabilities, but also degrade cellulose over a wide range of conditions.
Most biofuels used today are made from the fermentation of starch from corn kernels. That process, although simple, is costly because of the high price of the corn kernels themselves.
Agricultural waste, such as corn stover (the leaves, stalks, and stripped cobs of corn plants, left over after harvest), is cheap. These materials are largely composed of cellulose, the chief component of plant-cell walls. Cellulose is far tougher to break down than starch.
An additional complication is that while the fermentation reaction that breaks down cornstarch needs just one enzyme, the degradation of cellulose requires a whole suite of enzymes, or cellulases, working in concert.
Arnold and Caltech postdoctoral scholar Pete Heinzelman created the 15 new enzymes using a process called structure-guided recombination.
Using a computer program to design where the genes recombine, the researchers “mated” the sequences of three known fungal cellulases to make more than 6,000 progeny sequences that were different from any of the parents, yet encoded proteins with the same structure and cellulose-degradation ability.
After analysing the enzymes encoded by a small subset of those sequences, the researchers could predict which of the more than 6,000 possible new enzymes would be the most stable, especially under higher temperatures (a characteristic called thermostability).
“Enzymes that are highly thermostable also tend to last for a long time, even at lower temperatures. And, longer-lasting enzymes break down more cellulose, leading to lower cost,” said Arnold.
Using the computer-generated sequences, researchers synthesized actual DNA sequences, which were transferred into yeast in Arnold’’s laboratory. The yeast produced the enzymes, which were then tested for their cellulose-degrading ability and efficiency.
Each of the 15 new cellulases was more stable, worked at significantly higher temperatures (70 to 75 degrees Celsius), and degraded more cellulose than the parent enzymes at those temperatures.
“This is a really nice demonstration of the power of synthetic biology,” said Arnold.
The study is published in the early edition of the Proceedings of the National Academy of Sciences. (ANI)

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